Centrifugal solids dryer



June 9, 1964 P, GQOCH 3,136,721

CENTRIFUGAL SOLIDS DRYER Filed March 51, 1961 5 Sheets-Sheet 1 INVENTOR. FRED P. GOOCH BVWGM ATTORNEY 3 Sheets-Sheet 2 Filed March 31, 1961 R Y mm u we R vw m. m P a m D N\ N\ E F June 9, 1964 GOQCH 3,136,721

CENTRIFUGAL SOLIDS DRYER Filed March 31, 1961 3 Sheets-Sheet 3 Fig. 3

. INVENTQR. FRED P. G CH ATTO RNEY l ay United States Patent 3,136,721 CENTRIFUGAL SOLIDS DRYER Fred P. Gooch, Media, Pa., assignor to Pennsalt Chemicals Corporation, a corporation of Pennsylvania Filed Mar. 31, 1961, Ser. No. 99,855 3 Claims. (Cl. 210-376) This invention pertains to centrifugal machines of the type in which liquid and solid material are separated by centrifugal force. The invention pertains more particularly to centrifugal machines of the type that employ perforated rotors or baskets through the walls of which the liquid escapes during its separation from the solid material, and from which the solid material is discharged over a peripheral edge on the rotor.

In prior art centrifugal machines of this type, the rotors are variously shaped, and various forms of impeller mechanisms are employed to advance the solid material longitudinally toward the discharge edge for solid material. When the rotor is frusto-conical in shape, such mechanisms may function either to advance or to retard the flow of solid material over theperforated surface of the rotor, depending generally upon the relation between the angle of repose of the solid material and the angle between the perforated surface and the axis of rotation.

The flow control mechanism frequently takes the form of a worm or screw, a plow, a piston or pusher, or similar device positioned close to the inner perforated surface of the rotor, and movable relative to its perforations. As a result of such relative movement, a grating or comminuting action is set up between the movable member and the perforated surface of the rotor, which tends to reduce the size of the solid particles or crystals moving over the perforated surface, thus producing fines which either escape along with the liquid, or if not, then becoming intermixed with the dried solids of larger particle size, or causing plugging of the perforations.

In prior art centrifuges having pistons or pushers for moving the solids longitudinally of the perforated rotor,

and particularly when the rotor is conical in shape, con

siderableditficulty is experienced in keeping the inner perforated surface of the rotor uniformlycovered with the solids being drained or dried. Moreover, none, insofar as I am aware, provide for continuous automatic feeding the slurry, without rather close attention to regulation of the flow, valve or other throttling device in the feed line being employed for the purpose. Furthermore, in many prior art centrifugal machines of the pusher type-there is a marked tendency, stemming from various causes, for the solids in the rotor to become unevenly distributed, thus 3,136,721 Patented June 9, 1964 ice v FIGURE 5 is a ,view illustrating a bar-type of filter screen.

Referring now more particularly to FIGURE 2, at is shown a centrifuge having a base 11 with legs 12 for contact with the floor or other surface. Mounted on base 11 are bearing housings 13 and 14 containing bearings 15 and 16, respectively, in which is journaled hollow drive shaft 17 having pulley 18 attached to one end and rotor 19 to the other. As illustrated, a spacer 21 is provided around shaft 17 between bearings 15 and 16.

Disposed within drive shaft 17 is shaft 22 journaled in bearings 23 and 24, and having a reciprocating mechanism 25 attached to one end and rotor 26 to the other, rotor 26 being positioned within rotor 19.

As illustrated, rotor 26 is provided with a hub 27 which 7 is attached to shaft 22 by any suitable means, such as shown.

As illustrated, rotor 19 is provided with a perforated frusto-conical section 34 attached to hub 32 on shaft 17, and a perforated cylindrical section 36, attached to seetion 34.

Cylindrical section 36 is shown provided with a plurality of inwardly projecting annuli 37, and annulus 38 at its outer end and an annular connection 41 by which cylindrical section 36 is connected to frusto-conical section 34. Mounted upon the inner surfaces of annuli 37 and 38, and upon a ledge 42 on annular connecting member 41, is a screen 43. Screen 43 is cylindrical in shape, and preferably is comprised of longitudinal bars 39 which may be held in position by any suitable means, such as by welding, onannuli 37 and 38 and member 41 to form a'screen, e.g. of the type illustrated in FIGURE 5. For clarity in illustration, only the lower bar 44 and the upper bar 45 are shown in full in FIGURE 2, the former in section. Any other screening construction maybe substituted.

Inner rotor 26 is shown provided with a screen 46 which conveniently, though not necessarily, is of relatively fine mesh, and preferably has a relatively smooth inner surface, the latter to avoid undue grinding or comminution of solids sliding over this screen. Screen 46 is shown secured to hub 27 by means'of circular plate 47 and screw 48, the latter engaging hub 27 so as to secure the inner circumferential edge of screen 46 between the outer circular edge of plate 47 and hub 27.

The outer circumferential edge of screen 46 is shown secured between flange 51 on fotor 26 and ring 52, ring causing the machine to become mechanically'out of bal-' ance. For this reason, it is necessary to limit the rotational speeds of these machines to prevent their becoming wrecked when such unbalance occurs.

To overcome these and other shortcomings inherent-in centrifugal machines of the prior art, a centrifugal niachine embodying new and distinctly dilferent principles for the automatic feeding of the slurry to the machine, and

for the advancement through and the discharge of solids from the machine, is provided by the present invention. 'Further features of the inventionwill become apparent to persons skilled inthe art as the specification proceeds,

to the accompanying drawings, in

52 being secured to flange 51 by any suitable means, such as bolts or screws, not illustrated. v

Ring 52 is'shown provided with a plurality of. laterally projecting circumferentially spaced brackets 53 which converge axially inwardly to support cake-levelling ring 54 to which brackets 53.may be securedby any suitable means, such as welding. It will be noted that whereas the outer circular edges of flange 51 and ring 52 are positioned relatively closely adjacent cylindrical screen 43, the outer circular edge of cake-levelling ring 54 is spaced from the inner surface of cylindrical screen 43, as illustrated at 55;

,Reciprocatingmeans 25 is comprised of a cylinder 61 hinged at 62 to support63 secured to base 11. Cylinder 61 .is-provided witha piston 64 secured to a piston rod 65 slidably journaled as illustrated at66, in end'67 of cylinder 61. Piston rod 65 is secured to a two-part block 68 to which end'il of shaft 22is' joined as by thrust bearing 72, and to which end '71 thrustbearing 72 is secured, as by shoulder 73 on end 71 which abuts against one side of thrust bearing72 and nut 74 which abuts ing another position of the pusher mechanism; and Y 1 against the other side of thrust bearing 72, nut 74 threadedly engaging end 71 to secure said thrust bearing to end 71. Thrust bearing 72, in turn, is secured between parts 75 and 76 of blo ck 68, e.g. as illustrated.

Referring now more particularly to FIGURE 1, it will be noted that a cross bar 77 is mounted on part 76 of block 68, and it may be secured thereto by any suitable means, such as by welding. Cross bar 77 is connected to a second cross bar 7% by means of rods 81 and 82 which pass through and are slidably mounted in guide posts 83 and 84, respectively, said guide posts being mounted on frame 11.

Mounted centrally in cross bar 78, such as by welding, and extending inwardly into rotor 26, is feed tube support 35 (FIG. 2) through which feed tube 86 passes and extends further inwardly into rotor 26, as well as further outwardly beyond bar 73, e.g. as illustrated. Feed tube 86 may be adjustably secured relative to feed tube support 35 in any desired manner. As shown, a yoke 88 is secured, such as by welding, to feed tube 86, and is made adjustable laterally relative to bar 78, such as by adjusting mechanism 99, thereby to adjustably position tube 86 relative to support 85.

Secured to the inner end of feed tube 86 is annulus 87 which together with feed tube support 85 and feed tube 36 is maintained non-rotating.

Spray pipe 91 passes inwardly into rotor 19 through cross bar 73 in which it is secured, said spray pipe making a right angle turn (FIGURE 2) toward the inner periphery of rotor 19, and terminating with a nozzle 92, the latter spaced from the inner periphery of rotor 19, e.g. as illustrated in FIGURE 2.

A flexible teed hose 93 for slurry is shown connected to feed tube 86, and a feed hose for spray liquid 94, e.g. water, is shown connected to spray pipe 91.

Rotor 19 is shown surrounded by a casing 95, a rotary seal 96 being provided between rotor 19 and casing 95 at one end. Through the other end 97 of casing 95 feed tube support 85 and feed tube 36 extend inwardly. If desired, the lower half 98 of the metal of end 97 surrounding support 85 may be bent outwardly and the upper half 99 bent inwardly, as illustrated, to insure that any materials discharged from rotor 19 and striking end 97 will remain within casing 95. Casing 95 is illustrated as being equipped with circumferential baffles 101 and 102, the former positioned approximately in the plane of the outer end of rotor 19, and the latter, within rough approximation, being positioned in the plane of ring 52 when in the position shown in FIGURE 2. Bafiles 101 and 102 divide the interior of casing 95 into hoppers 103, 104 and 105 having outlets at their respective bottoms illustrated at 106, 107 and 108, respectively.

As previously pointed out, in the operation of centrifuge 10, rotor 26 is reciprocated axially relative to rotor 19, reciprocating mechanism 25 being employed for the purpose.

As seen in FIGURE 2, piston 64 of reciprocating mechanism 25 has been moved to the right, thus being caused by applying fluid pressure in cylinder 61 to the left of piston 64 through portlll, fluid pressure to the right of piston 64 being released through port 112. Rotor 26 is now in its right-hand position relative to rotor'19 as seen in FIGURES 2 and 4.

To cause piston 64 to move to the left, as seen in FIG- URE 2, fluid pressure is applied to the right-hand end of piston 64 through port 112, fluid pressure to the left of piston 64 being released through port 111. The result is that fluid pressure is brought to bear in the right-hand end 'of cylinder 61, which moves rotor 26 to the left from the position shown in FIGURES 2 and 4, the new position being illustrated in FIGURE 3.

Any means known in the art may be employed for applying pressure alternately to opposite sides of piston 64-, while releasing fluid pressure on the non-pressure side. For purposes of illustration, ports 111 and 112 are illustrated diagrammatically in FIGURE 1 as being connected to a four-way valve 113 having a lever 121 which is actuated reciprocatingly by a timer 114. Fluid pressure is delivered to valve 113 through line 115 by rotary pump 116 which in turn is connected through line 117 to fluid source 118, such as of oil. Pressure release line 119 connects valve 113 with fluid source 118 for the return of released fluid to source 118.

As illustrated, valve 113 is in a position connecting line 115 to port 111, and line 119 to port 112, the result being that piston 64 and rotor 26 are in their furthermost positions to the right as seen in FIGURE 2, rotor 26 also being shown in this position in FIGURE 4. To move piston 64 and rotor 26 to the left, valve 113 may be moved by lever 121 so as to connect line 115 to port 112, and line 119 to port 111, as will be obvious.

As will be well understood by persons skilled in the art, timer 114 may be made to operate valve 113 to alternately supply fluid under pressure to ports 111 and 112, while at the same time releasing pressure in the other of the two lines, thus causing piston 64 and rotor 26 to reciprocate axially relative to rotor 19.

Timers of the type illustrated at 114 are Well known. If desired, valve 113 may be operated manually by disconnecting timer 114 from lever 121, and reciprocating said lever 121 by hand.

Any other means for reciprocating rotor 26 relative to rotor 19 may be substituted.

In the operation of the centrifuge of the invention, rotor 19 is driven, e.g. by belts 33 applied to pulley 18. Rotor 2-6 follows the rotation of rotor 19 merely by friction between the parts, assisted by the flow of solids from rotor 26 into rotor 19. This makes unnecessary a mechanical connection between rotors 19 and 26 for the driving of rotor 26 from rotor 19, although such connection may be provided, if desired, as will be obvious.

A mixture of liquid and solids, e.g. in slurry form, is fed into rotor 26 through feed pipe 86. The mixture enters the space between annulus 87 and plate 47, and due :to the relative rotation between the adjacent surfaces of annulus 87 and plate 47, the mixture flows outwardly into rotor 26 around the circular periphery of annulus 37 which controls the depth of the mixture in rotor 26 at the smaller end of rotor 26. The same or similar manner of feed is described in my co-pending application, now Patent 3,087,621, issued April 30, 1963.

The mixture of liquid and solids slides along rotor 26 over screen 46, during which the liquid accompanying the solids is centrifugally separated, said liquid passing outwardly through screen 46, then through the perforations in rotor 26, and finally through the perforations in rotor 19, to be collected in hopper from which it is withdrawn through outlet 108.

The solids, now freed from all but surface-moistening liquid, continue their sliding movement, and reach cakelevelling ring 54. Due to the reciprocation of rotor 26 and its appurtenances, the solids continue their movement to the left as seen in FIGURE 2, but now around the peripheral edge of cake-levelling ring 54 to form a cylindrical cake of more or less uniform depth, as illustrated, the depth or thickness of solids at ring 54 customarily being greater than the width of annular space 55, or at least of sloping surface relative thereto.

A washing liquid may now be applied to the solids, if desired, such as through pipe 91 and nozzle 92, the wash liquid after passing through the cake of solids flowing outwardly through screen 43 and the adjacent perforations in rotor 19 to be collected in hopper 1114 from which the wash liquid is withdrawn through the outlet 107.

The solids continue their movement to the left as seen in FIGURE 2, and upon being separated from wash liquid, in consequence of such movement to the left while in rotor 19, are discharged into hopper 103 from which they are withdrawn through-outlet 106.

The movement of the solids tothe left in FIGURE 2, as above described, and the cake-levelling action also as above described, are the result of'the axial reciprocation of rotor 26 and its appurtenances relative to rotor 19. This can be more clearly seen upon reference to FIG- URES 3 and 4, of which FIGURE 4 illustrates the position of the solids when rotor 26 is in the position relative to rotor 19 as illustrated in FIGURE 2.

No attempt is made to show the solids in their exact positions in the drawings, for this is subject to variation depending among other things upon differences in crystal size and composition, and other factors.

In FIGURE 3, cake leveller 54 and ring 52 are shown as having been moved to the left from their respective positions in FIGURE 4, the distance X for ring 54 and the distance Y for the ring 52, these distances being equal. Upon the movement of ring 52 from the position shown in FIGURE 4 to the position shown in FIGURE 3, solids are pushed to the left in rotor 19 toward its discharge end. Cake-levelling ring 54 and rotor 26 are simultaneously moved to the left. Upon the return stroke to the position shown in FIGURE 4, the ring 54 performs a cake-levelling action, and a void is created at the left-hand face of ring 52, which is immediately filled with solids sliding down screen 46.

Thus it will be seen that upon movement of the re ciprocating mechanism to the left as seen in FIGURE 2, solids are discharged from rotor 19, whereas, upon its movement to the right, a void is created about the discharge end of rotor 26, which void is immediately filled by solids that discharge from rotor 26, the cake-levelling action of ring 54 functioning to produce a uniform cylindrical cake in rotor 19. i

It will be noted that cross bar 78 in view of its connection to cross bar 77 through rods 81 and 82 follows the reciprocation of rotor 26, thus maintaining a constant spacing between annulus 87 and plate 47, both shown positioned axially of rotor 26. This spacing is preferably made adjustable such as by making feed tube 86, shown axially positioned, longitudinally slidable in its support 85, also shown axially positioned, feed tube 86 being secured in adjusted position by any suitable means, such as above described.

Due to the relative rotational movement between annulus 87 and plate 47, the mixture of solids and liquid is fed radially outwardly into rotor 26 uniformly and without the attendant clogging which frequently results when corresponding parts are rotated at the same speed, or held stationary. ,The reason for such clogging is not fully understood, but is believed to be due at least in part to the packing or clogging tendency of mixtures of liquid and solid when the flow thereof is subjected to change 'in direction, e.g. of 30, or more, and particularly when simultaneously subjected to centrifugal force. The relative rotation between annulus 87 and plate 47 keeps the mixture in a constant state of motion which counteracts clogging tendencies. Moreover, this relative rotation has another very important result in that it maintains the rate of fiow'of feed into the centrifuge constant, to a large degree independently ofthe pressure on the mixture in the feed pipe 86. The latter makes it possible to feed by gravity under any desired head, or by pump pressure, or otherwise, as desired, without ma terially influencing the rate .of-feed of mixture into the rotor 26. t p

As shown and described, spray nozzle 92 reciprocates with the rotor 26, thus providing a reciprocating rinse for the cake of solids whichis preferred in most ,instances, but whichis by no means essential.-, In fact means for rinsing maybe dispensed with'entirely, if desired for any reason. I v

i As an example of the outstanding advantages to be derived upon theuse of the invention, reference is made to a run with a machine in which the cylindrical portion of the outer rotorhad an inner diameter of approximately 11 inches. The speed ofrotation was 27 00"r.p.m., and a slurry of salt (NaCl) crystals in mother liquor 6 90 cycles per minute, a cycle comprising a complete forward and backward movement. The reciprocating dis tance was inch, and the cake thickness in the cylin- V drical portion of the outer rotor was inch. The

residual moisture in the separated salt crystals was less than 2% by weight.

In another run in the same centrifugal machine, the rotor was operated at 2200 rpm. The slurry contained ice crystals in concentration of 30% solids by weight, the slurry resulting from the concentration of orange juice by a low temperature method. The slurry was fed to the machine at the rate of 2400 pounds per hour based on the dry weight of ice crystals. The reciprocating rate was 80 cycles per minute, and the reciprocating distance was 1 inch. The cake thickness in the cylindrical portion of the outer rotor was /2 inch. Mother liquor was present in the separated ice crystals in concentration of less than 500 parts per million.

Many other runs cogently demonstrate the new and unexpected results flowing from the invention.

Many advantages are afforded by the construction and operation of the centrifuge shown and described. One advantage is the ability to maintain acake of solids of virtually nonchanging configuration on the frusto-conical surface of rotor 26 at all times, this cake being auto matically replenished as the drained solids move on to the cylindrical screen 43, by the automatic feed afforded through the relative rotational movement between annulus 84 and plate 47 which normally are maintained uniformly spaced axially during operation.

Moreover, the reciprocation of frusto-conical rotor 26 feeds the mass forward, i.e. to the left as seen in FIGURE 2, with a minimum of. grating or comminuting action on screen 46, even though the plane angle between the axis of rotation and a straight line touching the inner surface of rotor 26 is significantly less than the average angle of repose of the slurry being processed, which is highly preferred, the angle of repose being herein generally con sidered as the maximum angle with the horizontal at which the slurry will retain its position without tending to slide, it being understood that the moisture content and the distributionof fine and coarse particles have an effect on the value of this angle. I

The reason for this is believed to be due to the effects of inertia, i.e. the tendency of the slurry to continue its movement to the left as seen in FIGURE-2 when rotor 26 ceases to move to the left at the end of its stroke, and, as to any slurry at rest atthe end of such stroke, its tendency, due to inertia, to continue to remain at rest. Sudden stops, as contrasted to deceleration prior to stopping, accentuates the former of these two effects, and is readily obtained, e.g. by the use of a bumper stop, or the use of a liquid for operating cylinder 61, with a sudden closing of a valve on the liquid release side, e.g. at

slurry being 50% by weight. The reciprocation rate was port 111 as seen in FIGURE 2. A sudden stop, equivalent to the use of a bumper, is obtained bypermitting piston 64- to strike, with force, the left inner end of cylinder 61. Sudden reversals to the right, such as by bringing a liquid to bear with high or full .force suddenly in the left hand end of cylinder 61, as seen'in FIGURE 2, accentuates the latter of these two effects. Such sudden reversals may be brought about by a rapid movement of valve 113 to bring aliquid under high or full pressure to bear quickly on "piston64 through portlll at the end of the left hand stroke.

Thus the plane angle. between theaxis and the frustoconical inner surface of rotor 26, or, if a combination of frusto-conical surfacesis employed,"the smallest plane angle between the axis and any such surface, of less than 35, e.g. of 25, has been found highly satisfactory for a large number of different slurries; It is preferred, however, not to use angles below 15 and more, particularly not below 20.

The use of such angles makes it possible to hold the slurry in the pre-draining step, i.e. in rotor 26, for any 7 6' esired length of time, for in such instances the rate of advance is, at least for far more than the most part, dependent upon the rate of reciprocation of rotor 26, although larger angles may be employed with the realization of other advantages of the invention.

The rate of reciprocation may be varied over a wide range, and is a matter of choice by the operator to obtain the desired effect.

The pre-draining which takes place in rotor 26 prepares the mass excellently for the movement of the solids, without buckling or channeling, over cylindrical surface 43 of rotor 19. This and the cake-levelling action of ring 54 insures the maintenance of a uniformly shaped cake on the cylindrical surface of rotor 19 throughout the operation of the centrifuge.

These factors are of outstanding importance in avoiding the development of undue unbalance during the operation of the centrifuge.

The fact that the solids are relatively dry as they pass around the outer periphery of cake-levelling ring 54 insures that these solids will maintain their cylindrical form during the push stroke that moves them to the left as seen in FIGURE 2.

Many prior art centrifuges have many shortcomings in the foregoing respects, making it necessary to limit the rotational speed to prevent their becoming wrecked when going out of balance.

Since the solids in rotor 19 maintain their cylindrical form, good rinsing is made possible, and because the cylindrical cake is relatively dry it does not compact, and thus permits better draining during rinsing.

Since the cylindrical cake is usually virtually as dry as can be obtained by the application of centrifugal force, i.e. in the pre-draining step carried out in rotor 26, the cylindrical portion of rotor 19 need not be perforated, if the steps of rinsing is to be eliminated. In such cases, only the portion of rotor 19 positioned radially outwardly from rotor 26 need be perforated, or otherwise constructed, to permit passage therethrough of the liquid thrown off from rotor 26.

Crystal grinding and pulverization are reduced to a virtual minimum, and thus losses due to the discharge of fine crystals along with the liquid are reduced to a virtual minimum.

Moreover, the new centrifuge of the invention is simple in construction in that it eliminates, among other things, a plow for the movement of solids, a gear box or other coupling to effect relative movement between a rotor and a plow, and other complications attendant upon the relative movement of rotating impeller mechanisms and rotors.

w it is, of course, to be understood that many variations in structure are possible, as will be readily recognized by persons skilled in the art. For instance, the juxtaposed or adjacent surfaces afforded by members 47 and 87 while shown planar and equidistant or generally parallel, may have other shapes and relationships, provided that there is relative rotation therebetween. It also will be recognized that rotor 19 need not be in part frusto-conical as illustrated, and that rotor 26 may have other shapes,

or a combination or plurality of shapes, whether frustoconical, curved in cross-section, or otherwise.

Moreover, that portion of rotor 19 which has been particularly described herein as cylindrical, which is highly preferred for the reasons given, may broadly speaking depart somewhat from the cylindrical shape, e.g. it may be frusto-conical with the discharge end (at the left in FIG. 2) having the larger diameter, provided that the angle of repose of the solids, as above defined in connection with rotor 26, is not exceeded, so that the solids will not slide upon reaching rotor 19, requiring the pushing action for their discharge. Thus the largest plane angle between the axis and such frusto-conical inner surface preferably should not exceed 35, e.g. 25, and, of course, may be as small as desired, including 0, the latter being the case when the cylindrical shape is employed, the axis and the line touching the inner surface in such case being parallel. Other variations will suggest themselves to persons skilled in the art upon becoming familiar with the invention.

Therefore, having particularly described the invention, it is to be understood that this is by way of illustration and not of limitation, and that changes, omissions, additions, substitutions and/or other modifications may be made without departing from the spirit thereof. Accordingly it is intended that the patent shall cover by suitable expression in the claims the various features of patentable novelty that reside in the invention.

I claim:

1. In a centrifuge the combination comprising a first rotor having a perforate wall, a second rotor having a frusto-conical perforate wall and disposed within said first rotor, said first rotor having an open end for the discharge of solids, said second rotor having its larger end facing the open end of said first rotor and terminating axially inward of said open end, said second rotor having an outer periphery terminating close to said first-named wall, means for rotating said rotors and means for reciprocating said second rotor, the means for rotating the second rotor extending away from the open end of the first rotor, an axially transverse inner surface on the smaller end of the second rotor, an axial, non-rotating feed conduit providing a cylindrical space for the passage of feed and extending in through the open end of the first rotor and having its outlet end positioned adjacent to and spaced from said transverse inner surface, an outwardly extending annulus rigidly secured about the outlet end of said feed conduit to present an annular surface opposing said first-named surface, the periphery of said annulus being uniformly spaced from the inner surface of the second rotor, means holding said second rotor and said feed conduit against relative axial movement, a cake-leveling ring mounted on said second rotor and spaced outward from the larger end thereof and held against relative axial movement with respect thereto, the ring having a circular outer edge and being of lesser radius than the inner surface of the wall of the first rotor to provide a space between said ring and said surface for the passage of solids, whereby the annulus about the outlet end of the feed tube and the cake-leveling ring both being held in unchanging axial relation to the second rotor serve to distribute the solids evenly over the perforate walls of the rotors without plugging or unbalance.

2. The centrifuge of claim 1 wherein said surfaces lie in closely spaced parallel planes respectively, both planes being perpendicular to the axis.

3. The centrifuge of claim 1 wherein the wall of the first rotor comprises a plurality of spaced parallel bars parallel to the axis of the first rotor.

References Cited in the file of this patent UNITED STATES PATENTS 1,839,941 Zelezniak Jan. 5, 1932 2,685,370 Ruegg Aug. 3, 1954 2,828,021 Ruegg Mar. 25, 1958 2,872,045 Wirth et al. Feb. 3, 1959 2,899,065 Irving Aug. 11, 1959 3,087,621 Gooch Apr. 30, 1963 FOREIGN PATENTS 590,969 Great Britain Aug. 1, 19 

1. IN A CENTRIFUGE THE COMBINATION COMPRISING A FIRST ROTOR HAVING A PERFORATE WALL, A SECOND ROTOR HAVING A FRUSTO-CONICAL PERFORATE WALL AND DISPOSED WITHIN SAID FIRST ROTOR, SAID FIRST ROTOR HAVING AN OPEN END FOR THE DISCHARGE OF SOLIDS, SAID SECOND ROTOR HAVING ITS LARGER END FACING THE OPEN END OF SAID FIRST ROTOR AND TERMINATING AXIALLY INWARD OF SAID OPEN END, SAID SECOND ROTOR HAVING AN OUTER PERIPHERY TERMINATING CLOSE TO SAID FIRST-NAMED WALL, MEANS FOR ROTATING SAID ROTORS AND MEANS FOR RECIPROCATING SAID SECOND ROTOR, THE MEANS FOR ROTATING THE SECOND ROTOR EXTENDING AWAY FROM THE OPEN END OF THE FIRST ROTOR, AN AXIALLY TRANSVERSE INNER SURFACE ON THE SMALLER END OF THE SECOND ROTOR, AN AXIAL, NON-ROTATING FEED CONDUIT PROVIDING A CYLINDRICAL SPACE FOR THE PASSAGE OF FEED AND EXTENDING IN THROUGH THE OPEN END OF THE FIRST ROTOR AND HAVING ITS OUTLET END POSITIONED ADJACENT TO AND SPACED FROM SAID TRANSVERSE INNER SURFACE, AN OUTWARDLY EXTENDING ANNULUS RIGIDLY SECURED ABOUT THE OUTLET END OF SAID FEED CONDUIT TO PRESENT AN ANNULAR SURFACE OPPOSING SAID FIRST-NAMED SURFACE, THE PERIPHERY OF SAID ANNULUS BEING UNIFORMLY SPACED FROM THE INNER SURFACE OF THE SECOND ROTOR, MEANS HOLDING SAID SECOND ROTOR AND SAID FEED CONDUIT AGAINST RELATIVE AXIAL MOVEMENT, A CAKE-LEVELING RING MOUNTED ON SAID SECOND ROTOR AND SPACED OUTWARD FROM THE LARGER END THEREOF AND HELD AGAINST RELATIVE AXIAL MOVEMENT WITH RESPECT THERETO, THE RING HAVING A CIRCULAR OUTER EDGE AND BEING OF LESSER RADIUS THAN THE INNER SURFACE OF THE WALLOF THE FIRST ROTOR TO PROVIDE A SPACE BETWEEN SAID RING AND SAID SURFACE FOR THE PASSAGE OF SOLIDS, WHEREBY THE ANNULUS ABOUT THE OUTLET END OF THE FEED TUBE AND THE CAKE-LEVELING RING BOTH BEING HELD IN UNCHANGING AXIAL RELATION TO THE SECOND ROTOR SERVE TO DISTRIBUTE THE SOLIDS EVENLY OVER HE PRFORATE WALLS OF THE ROTORS WITHOUT PLUGGING OR UNBALANCE. 